In general, the ion beam sputtering process involves the use of a low energy plasma source in a magnetic field which develops a neutralized ion beam with the ion energy, direction and current density all independently controllable and all independent of the type of target used. The plasma is produced by direct current electron bombardment of a low pressure gas, typically inert, but which may have a small percentage of reactive gases.
Generally, any target material which can be physically placed in a vacuum chamber can be sputtered by this process. This includes powders and composite targets, as well as elemental materials. In depositing a film of a given chemical composition, where the target is relied on as the primary source of material, it is accepted practice to prepare the target from a given composition. The target source is commonly prepared by mixing the desired proportions of chemical reagents and pressing the powders together at either elevated or room temperature. However, where multi-component targets are utilized, such effects of ion bombardment as sputtering, formation of an altered surface layer, enhanced diffusion, surface texturing, compound formation and phase transformation may strongly influence the resultant film that is deposited on a substrate. Further, the film composition is not necessarily the same as the target composition due to differences in ion sputtering coefficients and film sticking coefficients.
The prior art has relied on making several iterations of target materials to achieve film depositions of desired chemical composition. This is an expensive and time consuming empirical procedure and has not been wholly satisfactory in use. An alternative approach to depositing multi-component films used in the prior art is to allow the ion beam to strike a segmented target.
It is known to use a multi material segmented target such as reported by P. Reinhardt et al., Thin Solid Films 51, 99 (1978) where the film composition was controlled by lateral positioning of the targets in the beam to sputter varying fractions of the two targets, thereby allowing the film resistivity to be varied over a range of magnitude. Limitations of this procedure are that elemental sputter yields in alloys or components and that the sputter yield ratios in alloys may be strongly composition dependent. Therefore, in prior art processes, thin film deposition using ion sputtering, the final film composition is difficult to predict.
In U.S. Pat. No. 4,915,810 to Kestigian et al. a solution to the above described process limitations is proposed where a target is comprised of a composite matrix of material to be deposited upon a substrate and the target includes a plurality of openings where each of the openings have a plurality of plugs of predetermined composition adapted for a press fit into corresponding openings in the target. The ions are made to collide against the target thereby liberating particles from the target into an inert low pressure gas in the chamber which are then deposited onto a substrate. The plugs may be arranged in a particular pattern and the target and plugs therein may be made of a pre-selected composition to yield the desired thin film coating over the substrate.
In U.S. Pat. No. 6,852,201 to Hermeler et al. it is taught to shape the top surface of the plugs in such a way that the sputtering rate for each metal used in the sputtering process can be selected to yield the desired composition of the layer being applied.